Compound Interest Calculator
See how your savings grow — and how much of the final balance is pure interest.
Estimates for educational purposes only — not financial, tax, or investment advice.
How compound interest works
Compound interest is interest earning interest. Each period your balance grows, and the next period's interest is calculated on that larger balance. The longer your money compounds and the more you add each month, the more dramatic the snowball — which is why starting early matters more than starting big.
Why the 'interest earned' line matters
This calculator separates what you put in from what the market did. Over decades, the interest portion often dwarfs your contributions — a $300/month habit at 7% can turn into far more than the sum of the deposits. Adjust the return rate to see how sensitive the outcome is to even one percentage point.
Frequently asked questions
Is compound interest monthly or yearly?
This calculator compounds monthly, which matches most savings and investment accounts. More frequent compounding produces a slightly higher balance than annual compounding at the same rate.
What return rate should I use?
Use a realistic long-term estimate. Broad stock-market averages have historically been around 7% after inflation, but returns vary year to year and are never guaranteed.